In his stories, Isaac Asimov avoided giving common real world names to his characters, instead most of the time he invented new names or new spellings to existing names. This gave us lots of memorable character names: Wendell Urth, Giskard Reventlov and Kelden Amadiro, Lodovik Antyook, Hari Seldon and the emperor Cleon I. A few characters have more commonplace names, such as Susan Calvin and Gregory Powell.

Did Isaac Asimov use any name word for two unrelated characters in his science fiction writings?

Let me set up some long arbitrary guidelines.

Only published stories written by Isaac Asimov count. Stories written by other writers but published in anthologies or journals by Asimov don't count. Stories in the Foundation universe written with Asimov's permission by other authors after his death don't count for this question either, despite that I like some of them. (Eg. Lodovik Trema has the same first name as Lodovik Antyook, but the former wasn't named by Asimov. Update: nope, the hero of Blind Alley is actually called Loodun Antyok, so the names differ.) I do count the three novels expanded by Robert Silverberg from Isaac Asimov's short stories though.

Only science fiction stories count, whether in the Foundation universe or outside. (Most of my examples are from the Robots and Foundation stories, but this is only because that's what I'm familiar with.) Interpret science fiction broadly, that is, any story that would be on-topic for this site is good. Novels or short stories both work. Non-fiction books, such as books on popular science don't count for this question, so that we stay on topic.

Any significant word in the name counts. Given names like Hari or Han or Peter, family names like Seldon or Delmarre, other parts of the name, or parts of which we can't tell the role from the stories, they are all ok if they appear in multiple unrelated character's name.

However, common prefixes or suffixes like Jr. don't count. In particular, the R. prefix in several robot character's names don't count.

Names of characters count no matter whether they are main characters or just incidental, seen live or just mentioned, living or dead before the start of the story. Any species counts: robots, humans, cepheids, whatever.

Names of real people, or of characters not original to Asimov's fiction but known from before him don't count, unless the name itself is original to Asimov's stories. (These are rare in Asimov's fiction, but eg. The Caves of Steel mentions a few characters from the Bible.)

Duplications that have an in-world reason don't count. This means that the same name shared by people in a family don't count, eg. it's no surprise that Raych Seldon shares Hari Seldon's family name. Similarly, it is explained in character in Robots and Empire that Eliah Baley is seen as a hero by many colonists, which is why many of them, including the character D. G. Baley, share his names.

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“In his stories, Isaac Asimov avoided giving common real world names to his characters, instead most of the time he invented new names or new spellings to existing names.”

No, this is only true for some of his stories. In many stories he used common names like Sam, Robert, Mike or Joe, so it's almost inevitable that several characters share the same first or last name.

First name: Just one example, Mike: Mike Shea (Marooned off Vesta), Michael “Mike the Slug” Maguire (The Magnificent Possession), Mike Donovan (Reason and other robot stories), Mike Manners (All the Troubles of the World), Myron “Mike” Ginsbook (The Holmes-Ginsbook Device), etc. Mike is also the nickname of a robot in Too Bad! and of a computer in Think!

Last name: The famous Susan Calvin shares her last name with Preston Calvin (The Weapon). There's a Doctor Hamilton Sloane in It’s Such a Beautiful Day and a Jim Sloane in Sure Thing. Boris Vernadsky occurs in Sucker Bait, and Larry Vernadsky in The Talking Stone

First name/last name:Heredity has a Professor Harvey and Old-fashioned a Harvey Funarelli.